High-harmonic generation (HHG) is one of the most fundamental topics in nonlinear optics[1]}, [2]}, [3]}.
Experimental progress from the perturbative to the nonperturbative regime in gaseous media has paved the way for developing novel optical devices for, e.g., generating short-wavelength attosecond pulses [4]}, [5]}, [6]}, [7]}, [8]}, [9]}.
Moreover, HHG in the nonperturbative regime has been experimentally observed in solids[10]}, [11]}, [12]}, [13]}, [14]}, [15]}, and ensuing studies have opened up a new field in condensed-matter science [16]}, [17]}, [18]}, [19]}, [20]}, [17]}, [22]}, [23]}, [24]}, [25]}, [26]}, [27]}, [28]}.
In contrast to gaseous media, HHG in solids has various inherent properties that are rooted in the crystallinity of the medium and may provide means of developing new optical devices that use HHG.
Thus, it is important to study the characteristics of HHG in various materials and to devise a control method that can provide a possible route to novel optical technology.
